Tape drives store a vast amount of digital information on rolls of magnetic tape and are often used to backup information stored in computer systems. An example of a tape drive is a linear tape open (LTO) drive.
In a typical LTO drive, magnetic tape is stored on a supply reel contained in a removable cartridge. Data on the tape, including servo information, is arranged in 128 or more parallel tracks. During operation, the tape is passed along a series of rollers, defining the tape path, to a non-removable take up reel in the drive. The tape passes in close proximity to an assembly of read heads and write heads. The heads must be accurately positioned over the desired tracks so data can be read or written without loss and without corrupting adjacent tracks. An actuator positions the head assembly by moving it across the width of the tape. As the magnetic tape passes by the heads, the tape may have a small side-to-side motion due to the tolerances of the tape and the rollers. During coarse positioning, the actuator moves the head assembly so that a read head is close enough to a desired track to read servo information. Subsequently, during fine positioning, the servo information is read from the track and sent to servo control circuitry, which then sends a signal to the actuator to move the head directly over the desired track and to follow the small side-to-side motion of the track as it passes by the head.
Conventional actuators in LTO drives are often constructed as an electromagnetic actuator in which the head assembly is moved by the electromagnetic force from a strong permanent magnet and an electrically conductive coil. The electromagnetic actuator requires a coarse position sensor to determine the location of the head array during course positioning. Once the head assembly is over the desired track, a continuous electric current through the coil, called either a holding signal or holding current, is required to hold the head assembly in place.